ISO or Image with discourse ready to go for a server boot

No. There are too many things that are required for a functioning site (host name, functing email for starters).

You can get a “free” install using https://dashboard.literatecomputing.com/ if you’ll join the Free Trial Group and don’t need my support to make it work. It’s pretty trivial for Digital Ocean and Mailgun (since the script spins up the droplet and configures mailgun), and harder if you elect not to use either of those services.